# Thread: evaluating a parabola in equation form.

1. ## evaluating a parabola in equation form.

I don't really understand how to do this question:

If parabola $\displaystyle y-2=a(x-3)^2$ goes through the point (2,0), what is the value of a?

I have been able to determine that its vertex is (3,2) meaning that 'a' must be negative.
However, I have no idea about how to derive a number....

2. Can't you simply sub in (2,0) for (x,y)?

$\displaystyle 0-2 = a(2-3)^2$

3. So I was overthinking it?
I see, so 'a' is -2?

4. Yes, and it fits in with your working that it must be negative.

You were told that the equation passes through that point so that point must be a solution for the equations. I thought it would be more complicated at first

5. Originally Posted by e^(i*pi)
Yes, and it fits in with your working that it must be negative.

You were told that the equation passes through that point so that point must be a solution for the equations. I thought it would be more complicated at first
Ah, I feel quite dim....
But I have learnt something, so its not so bad!

Thank you very much for your help!